I think when a guy wants to get his wife/GF/significant other interested in fly fishing the most important thing, in her mind, is to catch some fish. Try setting her up with one of your nicer rods and reels and spending a few hours on the lawn showing her how to cast will go a long way towards sustaining her interest. Then try going to a stream that has recently been stocked and put her in a good pool with an indicator, a couple of nymphs, and your mentoring until she catches a couple trout. Years ago I had my wife take a day long seminar given by the lady who owned Yellow Breeches Oufitters. She had fun, learned about basic stuff, and then went out to the Run and caught a brown on a Green Weenie.
Then we booked a trip to a private central PA stream for a long weekend and she had a ball catching nice browns and rainbows on nymphs. The weekend included a guide so I chatted with him to spend time with my wife and make sure she had a good time and to just leave me to my own devices for the weekend. I caught a ton of 15" - 20" browns and rainbows and she got her taste of FFing.
